1. Field of the Invention
The present invention relates generally to electrical generators, and more particularly, the present invention relates to an apparatus and method for limiting the peak speed of the motor at which power is generated.
2. Description of Related Art
An apparatus for control of generator output power is known including an exciting winding of a generator, a voltage regulator connected with the generator, which controls the output power of the generator by influencing the excitation current in the exciting winding of the generator.
An AC alternator, which produces an alternating voltage, is predominantly used in motor vehicles to supply electrical power. The alternating voltage produced by the alternator is rectified in a connected rectifying device for supplying direct-current consuming devices and for charging a battery. Since the output voltage of the generator depends considerably on the generator speed, a voltage regulator is used to provide the desired constant output voltage, which influences the excitation current of the generator, so that the generator voltage is held at a constant value, which in the typical motor vehicle power supply system is 14 volts D.C., despite considerable changes in the generator speed.
Since the number of electrical energy-consuming devices in motor vehicles is continually growing, the requirements for generators are always increasing. Particularly in winter, when window heaters are turned on in addition to the standard consuming devices or when the motor vehicle spends a longer time in city traffic, and also when the generator is operated at a slower rotation speed, energy supply problems develop. For this reason the current generated by the A.C. alternator has been increased, so that the power output of the generator is greater at the same voltage.
A starter/alternator typically requires operation over a relatively wide range of speeds. However, it is undesirable to provide power above a certain speed in the generation mode due to limitations in the microprocessor or position sensor, due to an increase in acoustic noise, and/or due to a decrease in system efficiency.
The need exists for a system and method to actively limit the top speed of the generator motor at which power is provided.
The present invention provides a system and method to smoothly limit the top speed of the generator motor at which power is provided. Since a starter/alternator is controlled by a microprocessor and the speed of the motor is known at all times, it is possible to actively limit the top speed of the motor at which power is provided in the generation mode.
In accordance with this invention, a system according to this invention is provided which consists primarily of an engine, which supplies mechanical power to a switched reluctance motor with position sensor, which delivers electrical power to an inverter. The inverter contains a digital signal processor (DSP) controller to control the delivery of electrical power to the battery in the generation mode. The system of this invention delivers signal information regarding motor speed and current from the switched reluctance motor with position sensor to the DSP controller and delivers signal information regarding current and voltage from the battery to the DSP controller.
In the preferred embodiment, implementation of the invention will be accomplished with the switched reluctance machine. The machine is attached to the engine in a belt-driven configuration with a pulley ratio (e.g., 2.5:1). The switched reluctance machine will have position sensing capability in order to monitor the position of the rotor in relation to the stator, and sensors to monitor the phase currents and bus current. A digital signal processor (DSP) will be used in order to meet the precise position-based control requirements. Therefore, since the position and current is monitored and controlled in real-time by the DSP, the power output in the generation mode can be actively reduced as the speed increases or disabled at a certain maximum speed.